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Marco L Fiorentini - One of the best experts on this subject based on the ideXlab platform.
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numerical modeling of erosion and assimilation of sulfur rich substrate by martian lava flows implications for the genesis of massive sulfide mineralization on mars
Icarus, 2017Co-Authors: Raphael J Baumgartner, Marco L Fiorentini, D Baratoux, Fabrice GaillardAbstract:Mantle-derived volcanic rocks on Mars display physical and chemical commonalities with mafic-ultramafic ferropicrite and Komatiite volcanism on the Earth. Terrestrial Komatiites are common hosts of massive sulfide mineralization enriched in siderophile-chalcophile precious metals (i.e., Ni, Cu, and the platinum-group elements). These deposits correspond to the batch segregation and accumulation of immiscible sulfide liquids as a consequence of mechanical/thermo-mechanical erosion and assimilation of sulfur-rich bedrock during the turbulent flow of high-temperature and low-viscosity Komatiite lava flows. This study adopts this mineralization model and presents numerical simulations of erosion and assimilation of sulfide- and sulfate-rich sedimentary substrates during the dynamic emplacement of (channelled) mafic-ultramafic lava flows on Mars. For sedimentary substrates containing adequate sulfide proportions (e.g., 1 wt% S), our simulations suggest that sulfide supersaturation in low-temperature ( 1400°C). The precious-metals tenor in the derived immiscible sulfide liquids may be significantly upgraded as a result of their prolonged equilibration with large volumes of silicate melts along flow conduits. The influence of sulfate assimilation on sulfide supersaturation in martian lava flows is addressed by simulations of melt-gas equilibration in the C-H-O-S fluid system. However, prolonged sulfide segregation and deposit genesis by means of sulfate assimilation appears to be limited by lava oxidation and the release of sulfur-rich gas. The identification of massive sulfide endowments on Mars is not possible from remote sensing data. Yet the results of this study aid to define regions for the potential occurrence of such mineral systems, which may be the large canyon systems Noctis Labyrinthus and Valles Marineris, or the Hesperian channel systems of Mars’ highlands (e.g., Kasei Valles), most of which have been periodically draped by mafic-ultramafic lavas.
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Use and calibration of portable X-Ray fluorescence analysers: application to lithogeochemical exploration for Komatiite-hosted nickel sulphide deposits
2016Co-Authors: Margaux Le Vaillant, Marco L Fiorentini, Louise Fisher, Stephen J. Barnes, Stefano CarusoAbstract:Portable X-Ray Fluorescence (pXRF) analysers allow on-site geochemical analysis of rock powders and drill core. The main advantages of pXRF analysis over conventional laboratory analysis are the speed of data collection and the low cost of the analyses, permitting the collection of extensive, spatially representative datasets. However, these factors only become useful if the quality of the data meets the requirements needed for the purposes of the study. Here, we evaluate the possible use of portable XRF to determine element concentrations and ratios used in exploration for Komatiite-hosted nickel sulphides. A portable XRF analyser was used to measure a series of chalcophile and lithophile element concentrations (Si, S, K, Ca, Ti, Cr, Fe, Ni, Cu, Zn, As, Sr, and Zr) of 75 samples from three Komatiite units associated with nickel sulphide ores in the Yilgarn Craton, Western Australia. Crucial steps in the study were the development of a strict calibration process as well as numerous data quality checks. The 670 analyses collected in this study were compared with conventional laboratory XRF data on discriminant diagrams commonly utilized in exploration for Komatiite-hosted nickel sulphides (Cr vs Ni and Ni/Ti vs Ni/Cr). After comparing the results obtained with pXRF during this study with the laboratory values, we can conclude that portable XRF analyses can be used for rapid assessment of the nickel sulphide prospectivity of Komatiites provided that strict control protocols are followed.
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use and calibration of portable x ray fluorescence analysers application to lithogeochemical exploration for Komatiite hosted nickel sulphide deposits
Geochemistry-exploration Environment Analysis, 2014Co-Authors: Margaux Le Vaillant, Marco L Fiorentini, Louise Fisher, Stefano CarusoAbstract:Portable X-Ray Fluorescence (pXRF) analysers allow on-site geochemical analysis of rock powders and drill core. The main advantages of pXRF analysis over conventional laboratory analysis are the speed of data collection and the low cost of the analyses, permitting the collection of extensive, spatially representative datasets. However, these factors only become useful if the quality of the data meets the requirements needed for the purposes of the study. Here, we evaluate the possible use of portable XRF to determine element concentrations and ratios used in exploration for Komatiite-hosted nickel sulphides. A portable XRF analyser was used to measure a series of chalcophile and lithophile element concentrations (Si, S, K, Ca, Ti, Cr, Fe, Ni, Cu, Zn, As, Sr, and Zr) of 75 samples from three Komatiite units associated with nickel sulphide ores in the Yilgarn Craton, Western Australia. Crucial steps in the study were the development of a strict calibration process as well as numerous data quality checks. The 670 analyses collected in this study were compared with conventional laboratory XRF data on discriminant diagrams commonly utilized in exploration for Komatiite-hosted nickel sulphides (Cr vs Ni and Ni/Ti vs Ni/Cr). After comparing the results obtained with pXRF during this study with the laboratory values, we can conclude that portable XRF analyses can be used for rapid assessment of the nickel sulphide prospectivity of Komatiites provided that strict control protocols are followed. Supplementary Material: is available at http://www.geolsoc.org.uk/SUP18706
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spatial variation in platinum group element concentrations in ore bearing Komatiite at the long victor deposit kambalda dome western australia enlarging the footprint of nickel sulfide orebodies
Economic Geology, 2013Co-Authors: Geoffrey J Heggie, Marco L FiorentiniAbstract:The detectable footprints of Komatiite-hosted nickel sulfide deposits are typically very small, but can potentially be enlarged by identifying subtle geochemical variations related to ore-forming processes in the host rocks. This study examines the spatial variability of whole-rock concentrations of platinum group elements (PGEs) within the host flow to massive nickel sulfide mineralization at the Long-Victor deposit, Kambalda dome (Western Australia), where a series of ore shoots occupy two subparallel channels, over a strike length of approximately 3,000 m. The basal Komatiite flow unit at Long-Victor contains a wide range of platinum group element concentrations and PGE/Ti ratios in S-poor rocks outside the ore shoots. About a third of the samples analyzed show evidence for either enrichment or depletion in PGEs, as estimated from mantle-normalized ratios of Pt/Ti, Pd/Ti, and Rh/Ti, relative to background values typical of those found in Neoarchean Munro-type Komatiites worldwide. The very strong correlations observed between Pt/Ti, Pd/Ti, and Rh/Ti testify to a primary magmatic origin of this signal. Depletion signatures are largely restricted to samples in the flanking environment within the basal flow, and are found both in spinifex-textured A-zone and cumulate B-zone samples. The strongest depletion signatures are preserved in the uppermost portions of the A-zone and decrease in magnitude with increasing depth from the stratigraphic top of the spinifex horizon downward. This is interpreted as the result of progressive flushing of the flow channel by PGE-undepleted lava subsequent to ore formation. Enriched signatures are largely restricted to cumulate rock types, and are found within both channels and flanks. The halo of anomalous PGE/Ti ratios, both depleted and enriched, extends more than 400 m from the cutoff of 0.4% Ni that defines the limit of disseminated ores, and is much more extensive and marked than anomalies defined by Ni concentrations, Ni/Cr ratios, or Ni/Ti ratios, which extend no more than 20 m beyond the disseminated ores themselves. The PGE enrichment halo is recognizable in rocks having no visible sulfide and having Ni values falling within the silicate background, and is attributed to the accumulation of small proportions of PGE-rich disseminated sulfide liquid formed at high R factors, with subsequent loss of S during hydrothermal alteration. Mapping of PGE/Ti ratios provides an effective and sensitive method for vectoring toward ore during mine-scale and prospect-scale exploration, and is potentially applicable to mafic systems as well as to Komatiites.
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Komatiite magmas and sulfide nickel deposits a comparison of variably endowed archean terranes
Economic Geology, 2012Co-Authors: Marco L FiorentiniAbstract:Komatiites are found in most Archean granite-greenstone terranes, but sulfide Ni mineralization associated with these rocks has a very biased distribution. The global endowment of sulfides Ni in Archean Komatiites is overwhelmingly dominated by the Kalgoorlie terrane of the Eastern Goldfields Superterrane in the Yilgarn Craton. The question of whether the Kalgoorlie terrane Komatiites possess any exceptional attributes which could explain this bias is addressed through an exhaustive compilation of geochemical data from this terrane and a number of others: the southeastern Youanmi terrane of the Yilgarn Craton; the eastern terranes of the Eastern Goldfields superterrane (Kurnalpi, Burtville and others); and the Abitibi greenstone belt of the Superior province. High MgO Komatiite magmas, with MgO in the 25 to 30% range, are found in all the terranes sampled, but the proportion of these compositions appears to be higher in the Kalgoorlie terrane, and the abundance of strongly adcumulate olivine cumulates is much higher. Crustal contamination is apparently more extensive and advanced in the Kalgoorlie terrane than in all the others, but there is no systematic difference in the lithophile trace element (LILE) characteristics and degree of source depletion evident in the most primitive magmas from all the terranes. Consideration of variable-valency transition metals V and Cr indicates there are no systematic variations in oxidation state between the terranes and Komatiites uniformly evolved close to the quartz-fayalite-magnetite buffer. Platinum-group element (PGE) variations imply that Komatiites in all the terranes were emplaced sulfide undersaturated and were derived from sources with remarkably similar PGE contents. There is no evidence that the Kalgoorlie terrane magmas were in any way exceptional. The Forrestania and Lake Johnston Belts of the Youanmi terrane include the only known examples of Al-depleted Komatiites hosting significant Ni sulfide resources, and they are also the only Komatiites of this type that form adcumulate dunite bodies. The presence of adcumulate dunites, formed by high magma fluxes in central conduits, is the common feature between these belts and the Kalgoorlie terrane. Coupled with evidence for higher degrees of contamination in the Kalgoorlie terrane, and the availability of accessible crustal S sources, it appears that magma flux, rather than primitive magma composition, is the critical factor, and that craton-scale deep lithospheric structure is the ultimate control on the rate of magma supply between mantle source and crustal emplacement site. The Kalgoorlie terrane Komatiites were emplaced at exceptionally high rates, giving rise to well-developed long-lived magma conduits, either lava tubes or subvolcanic channelized sills, which are interpreted to be the essential condition for forming large deposits.
Robert Kerrich - One of the best experts on this subject based on the ideXlab platform.
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geochemistry of a komatiitic boninitic and tholeiitic basalt association in the mesoarchean koolyanobbing greenstone belt southern cross domain yilgarn craton implications for mantle sources and geodynamic setting of banded iron formation
Precambrian Research, 2013Co-Authors: Thomas Angerer, Robert Kerrich, Steffen HagemannAbstract:Abstract Komatiite–basalt magmatism and Algoma-type banded iron formation (BIF) of Archean greenstone terranes have common time series, but there are few constraints on the geodynamic setting in which BIF were precipitated. The ∼3.0 Ga Koolyanobbing greenstone belt (KGB), Southern Cross Domain, Yilgarn craton, exhibits an greenschist to lower amphibolite facies metamorphosed lithostratigraphic series, including four predominantly mafic to ultramafic volcanic sequences (S1–S4) with prominent BIF horizons (and local basal pyrite-dominated massive sulfide lenses) in between. Petrography, XRD, high-precision major, trace high field strength, and REE element chemistry of representative ultramafic and mafic rocks from S1, S2, and S3 are consistent with a komatiitic, boninitic, and tholeiitic basalt association. Komatiites are Al-depleted and Al-undepleted (Al2O3/TiO2 12–28 and (Gd/Yb)N, ≥1) endorsing a zoned plume and/or melting over a range of depths. The boninite-series rocks (Al2O3/TiO2 28–45 and (Gd/Yb)N, Pearce (2008) , implying a depleted, mildly heterogeneous, source for the mantle plume from which Komatiites erupted. Boninites lie parallel to and above the mantle array, in the field of intraoceanic arcs, in keeping with their inferred oceanic convergent margin setting. Ratios of Nb/Yb extend to lower and higher values than Komatiites implying a more heterogeneous upper mantle source of the subarc wedge. The KGB exhibits the first reported boninite-suite rocks in the Southern Cross Domain, Yilgarn craton. Conclusively, the komatiitic, boninitic, and tholeiitic basalt association suggests that BIF and basal massive pyrite lenses of the Koolyanobbing greenstone belt were precipitated from low-temperature submarine discharge of a seawater-dominated hydrothermal system driven by magmatic systems of a mantle plume erupting in a forearc convergent margin suprasubduction ophiolite.
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Komatiite basalt rhyolite volcanic associations in northern superior province greenstone belts significance of plume arc interaction in the generation of the proto continental superior province
Lithos, 1999Co-Authors: Pete Hollings, Derek A. Wyman, Robert KerrichAbstract:Abstract Archean greenstone belts from the northern Superior Province, ranging in age from 3.0 to 2.9 Ga, comprise an association of Komatiite–tholeiite sequences, some of which were erupted onto continental crust, intercalated with felsic volcanic rocks. Komatiites from the Uchi subprovince are characterised by variable LREE enrichment and negative Nb anomalies consistent with contamination of Munro-type Al-undepleted Komatiites by a felsic melt. The majority of Komatiites display variable HREE patterns and positive normalised V–Sc anomalies. Tholeiitic flows intercalated with the Komatiites typically have flat rare earth element (REE) patterns with variable Nb anomalies and high Th/Ce ratios, consistent with minor degrees of contamination by sialic crust. Two suites of felsic volcanic rock, Type 1 and Type 2, have been recognised intercalated with the Komatiite–tholeiite sequences. Both types display LREE enriched patterns and negative Nb and Ti anomalies, but Type 1 has strongly fractionated HREE patterns, whereas Type 2 HREE are generally flat and have elevated Ni and Cr contents. The predominant Type 1 rhyolite is directly comparable to southern Superior Province felsic volcanic rocks associated with oceanic arc sequences and inferred to be the products of oceanic slab melting. Type 2 rhyolite geochemical signatures may result from mixing of Type 1 rhyolites with tholeiitic magmas, or a contribution from mantle wedge sources located above the garnet stability field. The intercalation of Komatiites and arc-type felsic volcanic rocks is best explained by interaction between an ascending mantle plume and adjacent subduction zones.
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Boninite series: low Ti-tholeiite associations from the 2.7 Ga Abitibi greenstone belt
Earth and Planetary Science Letters, 1998Co-Authors: Robert Kerrich, Derek A. Wyman, J. Fan, Wouter BleekerAbstract:Abstract Boninite series volcanic flows, interfingered with Komatiites and tholeiitic basalts, occur at several localities in the ∼2.7 Ga Abitibi greenstone belt. Flows from Whitney Township, Ontario, have a compositional range of SiO2 44–60 wt%, MgO 24–7.4, Mg# 83–69, and Ni 930–200 ppm. Low TiO2 (0.14–0.31 wt%) but high Al2O3 (13–25 wt%) contents yield variably high Al2O3/TiO2 ratios of 48–100. These boninite series volcanics are characterized by fractionated HREE where Gd/Ybn 0.3–0.7; positive normalized Zr(Hf)/MREE anomalies, and Zr/Hf > 36; generally negative normalized Nb anomalies; and LREE depletion to enrichment (La/Smn 0.72–1.4). Flows with similar compositional affinities occur in the neighbouring Kidd Volcanic Complex and Tisdale volcanic group. Alteration, and/or contamination by continental crust can be ruled out as the cause of the distinctive and coherent compositions. If the areally extensive Komatiite–tholeiite association represents an ocean plateau derived from a mantle plume and the boninite series formed in a convergent margin, then the interfingering of Komatiite and boninite series flows may represent interaction of a plume with a subduction zone.
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geochemical characteristics of aluminum depleted and undepleted Komatiites and hree enriched low ti tholeiites western abitibi greenstone belt a heterogeneous mantle plume convergent margin environment
Geochimica et Cosmochimica Acta, 1997Co-Authors: J. Fan, Robert KerrichAbstract:A compositionally diverse suite of Komatiites, komatiitic basalts, and basalts coexist in the Tisdale volcanic assemblage of the late-Archean (∼2.7 Ga) Abitibi greenstone belt. The Komatiites are characterized by a spectrum of REE patterns, from low total REE contents (9 ppm) and pronounced convex-up patterns to greater total REE (18 ppm) and approximately flat-distributions. Thorium and niobium are codepleted with LREE. Komatiites with the most convex-up patterns have low Al2O3 (4.7 wt%) contents and Al2O3/TiO2(12) ratios; they are interpreted to be the Al-depleted variety of Komatiite derived from a depleted mantle source. Those Komatiites and komatiitic basalts with flatter REE patterns are characterized by greater Al2O3 (7.0 wt%) and near chondritic Al2O3/TiO2 (20) ratios; they are interpreted to be Al-undepleted Komatiites generated from trace element undepleted mantle. For the Komatiites and komatiitic basalts collectively, ratios are negatively correlated with , but positively with MgO and Ni. The spectrum of patterns is interpreted as mixing between Al, HREE, Y-depleted, and Sc-depleted Komatiites and Al-undepleted Komatiites in a heterogeneous mantle plume. Auminum-depleted Komatiites are characterized by negative Zr and Hf anomalies, consistent with majorite garnet-liquid D's for HFSE and REEs, signifying melt segregation at depths of >400 km. Tisdale Al-undepleted Komatiites and komatiitic basalts have small negative to zero Zr(Hf)/MREE fractionation, signifying melt segregation in or above the garnet stability field. Collectively, the Komatiites have correlations of and Hf/Hf∗ with , and hence the Zr(Hf)/MREE fractionations are unlikely to have stemmed from alteration or crustal contamination. Two types of basalts are present. Type I basalts are Mg-tholeiites with near flat REE and primitive mantle normalized patterns, compositionally similar to abundant Mg-tholeiites associated with both Al-undepleted and Al-depleted Komatiites in the Abitibi belt. They have absolute concentrations and ratios of most moderately and highly compatible elements comparable to N- MORB (Zr ∼79 vs. 74, Y ∼30 vs. 28, and ), but are relatively less depleted in highly incompatible elements and lack positive Nb or P anomalies. Type II basalts are relatively aluminous (Al2O3 ∼ 16 wt%), with high Al2O3/TiO2 (24–28) ratios. They are characterized by low Th, Nb, and LREE contents at eight to ten times chondrite, with slightly convex-up LREE patterns (), but strongly fractionated and enriched HREEs, Y, and Sc, where and consistently positive Zr(Hf)/MREEs anomalies. These basalts are tentatively interpreted as low-Ti tholeiites formed in a convergent margin setting with second stage melting, induced by fluids and melts enriched in incompatible elements and Zr(Hf) relative to MREEs, of a mantle source depleted during first stage melting. They are analogous to the Phanerozoic low-Ti tholeiite—boninite association. Accordingly the Tisdale volcanic sequence records a plume-convergent margin interaction. New analyses of Al-undepleted Komatiites from the classical locality at Pyke Hill in Munro Township confirm the presence of small positive anomalies of P, Zr, and Hf, with ratios generally < 36. These signatures are similar in spinifex and cumulate zones signifying that they are unlikely to have resulted from alteration. The data were generated by INAA and ICP-MS using both HFHNO3 dissolution and Na2O2 sinter. The lack of LREE enrichment with negative Nb, Ta, P, and Ti anomalies in any of the Tisdale or Munro Komatiites confirms an intraoceanic setting for the volcanic stage of the Western Abitibi greenstone belt.
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silicate perovskite and majorite signature Komatiites from the archean abitibi greenstone belt implications for early mantle differentiation and stratification
Journal of Geophysical Research, 1994Co-Authors: Qianli Xie, Robert KerrichAbstract:Three Komatiite-tholeiite sequences from the Archean Abitibi Southern Volcanic Zone (SVZ), which are separated by major terrane boundaries, show systematic differences in composition, rare earth element (REE) patterns and high field strength element (HFSE) /REE fractionation. Komatiites from Tisdale Township are Al-undepleted, with MgO = 12–24%, Al2O3/TiO2 = 13–17, CaO/Al2O3 = 1–1.3, and high Ni (722–1275 ppm) and Cr (1875–2820 ppm) contents. Mg-tholeiites and Fe-tholeiites are spatially associated with Komatiites. Both Komatiites and Mg-tholeiites have flat REE patterns [(La/Yb)n = 0.6–1.2, and Nb/Nb*, Zr/Zr*, and Hf/Hf* ≈ 1 (calculated using primitive mantle normalized values and adjacent REEs in the incompatibility sequence of elements in mid-ocean ridge basalt; MORB), suggesting that they may have formed by high-degree partial melting of primitive mantle materials with olivine as the main liquidus phase at shallow depths ( 1, consistent with having been derived from Mg-perovskite enriched sources at depths >700 km below the transition zone, whereas spatially associated tholeiites have (La/Yb)n = 1–2, and Nb/Nb*, Zr/Zr*, and Hf/Hf* ≈ 1, suggesting a shallow undepleted mantle source, distinct from the Komatiites. Komatiites and tholeiites from Boston Township are characterized by MgO = 11–29%, Al2O3/TiO2 = 4.5–5.4, CaO/Al2O3 = l.4–2.5, high Ni (203–3420 ppm) and Cr (194–1965 ppm) contents; Al, Sc, Y, and heavy rare earth element (HREE) depletion, and pronounced negative normalized Zr and Hf anomalies (Zr/Zr* and Hf/Hf* < 1), in accord with either partial melting of a majorite depleted mantle source or majorite fractionation during magma formation in the depth range of 300–600 km. The fractionated HFSEs and REEs of Munro - and Boston-area Komatiites indicate that these Archean Komatiites may have preserved some signatures of early mantle differentiation, which so far has only been inferred based on high-pressure experimental studies and theoretical predictions. Further geochemical studies of Archean Komatiites, especially precise multiple trace element analysis, combined with improved measurements of partition coefficients over a wide pressure range, will provide better understanding on early mantle differentiation, stratification, and the transition zone.
Ambre Luguet - One of the best experts on this subject based on the ideXlab platform.
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formation of high al Komatiites from the mesoarchean quebra osso group minas gerais brazil trace elements hse systematics and os isotopic signatures
Chemical Geology, 2016Co-Authors: D Van Acken, J E Hoffmann, J H D Schorscher, Toni Schulz, Alexander Heuser, Ambre LuguetAbstract:Abstract We report highly siderophile element data combined with Re–Os isotopes and major and trace elements of the ca. 2.7–3.0 Ga Komatiites from the Quebra Osso Group, Minas Gerais, Brazil. These Komatiites resemble the rare high Al-type, characterized by high Al2O3/TiO2 ratios (26.7–59.8). These geochemical similarities are shared with the 3.33 Ga Commondale and 3.26 Ga Weltevreden Komatiites from the eastern Kaapvaal Craton pointing to a similar origin of these suites. While anhydrous melting in an unusually hot mantle was inferred for the Weltevreden Komatiites, the Commondale Komatiites were suggested to have formed by hydrous, multi-stage melting. Significant depletion in LREE is coupled with subchondritic Re/Os, unradiogenic to radiogenic 187Os/188Os and fractionated HSE, with enrichments in Ru, Pt, and Pd over Os and Ir. The combination of these signatures suggests minor late-stage crustal influence. Potential late-stage alteration overprint, assimilation of ambient mantle material during magma ascent and complex phase relationships of HSE-hosting phases make it difficult to estimate the composition of the source of the Quebra Osso Komatiites and to place constraints on the nature of the late Archean mantle. However, the Quebra Osso Komatiites are unlikely to have formed in a single-stage plume setting or in a supra-subduction zone setting. Instead we suggest a multi-stage melting history of the Komatiite source to explain the origin of their peculiar geochemical characteristics, as has been suggested for other high-Al2O3/TiO2 Komatiite suites.
J E Hoffmann - One of the best experts on this subject based on the ideXlab platform.
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formation of high al Komatiites from the mesoarchean quebra osso group minas gerais brazil trace elements hse systematics and os isotopic signatures
Chemical Geology, 2016Co-Authors: D Van Acken, J E Hoffmann, J H D Schorscher, Toni Schulz, Alexander Heuser, Ambre LuguetAbstract:Abstract We report highly siderophile element data combined with Re–Os isotopes and major and trace elements of the ca. 2.7–3.0 Ga Komatiites from the Quebra Osso Group, Minas Gerais, Brazil. These Komatiites resemble the rare high Al-type, characterized by high Al2O3/TiO2 ratios (26.7–59.8). These geochemical similarities are shared with the 3.33 Ga Commondale and 3.26 Ga Weltevreden Komatiites from the eastern Kaapvaal Craton pointing to a similar origin of these suites. While anhydrous melting in an unusually hot mantle was inferred for the Weltevreden Komatiites, the Commondale Komatiites were suggested to have formed by hydrous, multi-stage melting. Significant depletion in LREE is coupled with subchondritic Re/Os, unradiogenic to radiogenic 187Os/188Os and fractionated HSE, with enrichments in Ru, Pt, and Pd over Os and Ir. The combination of these signatures suggests minor late-stage crustal influence. Potential late-stage alteration overprint, assimilation of ambient mantle material during magma ascent and complex phase relationships of HSE-hosting phases make it difficult to estimate the composition of the source of the Quebra Osso Komatiites and to place constraints on the nature of the late Archean mantle. However, the Quebra Osso Komatiites are unlikely to have formed in a single-stage plume setting or in a supra-subduction zone setting. Instead we suggest a multi-stage melting history of the Komatiite source to explain the origin of their peculiar geochemical characteristics, as has been suggested for other high-Al2O3/TiO2 Komatiite suites.
M Jayananda - One of the best experts on this subject based on the ideXlab platform.
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physical volcanology and geochemistry of palaeoarchaean Komatiite lava flows from the western dharwar craton southern india implications for archaean mantle evolution and crustal growth
International Geology Review, 2016Co-Authors: M Jayananda, Raymond A Duraiswami, K R Aadhiseshan, R V Gireesh, B C Prabhakar, Koweu Kafo, R NamrathaAbstract:ABSTRACTPalaeoarchaean (3.38–3.35 Ga) Komatiites from the Jayachamaraja Pura (J.C. Pura) and Banasandra greenstone belts of the western Dharwar craton, southern India were erupted as submarine lava flows. These high-temperature (1450–1550°C), low-viscosity lavas produced thick, massive, polygonal jointed sheet flows with sporadic flow top breccias. Thick olivine cumulate zones within differentiated Komatiites suggest channel/conduit facies. Compound, undifferentiated flow fields developed marginal-lobate thin flows with several spinifex-textured lobes. Individual lobes experienced two distinct vesiculation episodes and grew by inflation. Occasionally Komatiite flows form pillows and quench fragmented hyaloclastites. J.C. Pura Komatiite lavas represent massive coherent facies with minor channel facies, whilst the Bansandra Komatiites correspond to compound flow fields interspersed with pillow facies. The Komatiites are metamorphosed to greenschist facies and consist of serpentine-talc ± carbonate, actinoli...
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geochemical constraints on Komatiite volcanism from sargur group nagamangala greenstone belt western dharwar craton southern india implications for mesoarchean mantle evolution and continental growth
Geoscience frontiers, 2013Co-Authors: M JayanandaAbstract:We present field, petrographic, major and trace element data for Komatiites and Komatiite basalts from Sargur Group Nagamangala greenstone belt, western Dharwar craton. Field evidences such as crude pillow structure indicate their eruption in a marine environment whilst spinifex texture reveals their Komatiite nature. Petrographic data suggest that the primary mineralogy has been completely altered during post-magmatic processes associated with metamorphism corresponding to greenschist to lower amphibolite facies conditions. The studied Komatiites contain serpentine, talc, tremolite, actinolite and chlorite whilst tremolite, actinolite with minor plagioclase in komatiitic basalts. Based on the published Sm-Nd whole rock isochron ages of adjoining Banasandra Komatiites (northern extension of Nagamangala belt) and further northwest in Nuggihalli belt and Kalyadi belt we speculate ca. 3.2–3.15 Ga for Komatiite eruption in Nagamangala belt. Trace element characteristics particularly HFSE and REE patterns suggest that most of the primary geochemical characteristics are preserved with minor influence of post-magmatic alteration and/or contamination. About 1/3 of studied Komatiites show Al-depletion whilst remaining Komatiites and Komatiite basalts are Al-undepleted. Several samples despite high MgO, (Gd/Yb)N ratios show low CaO/Al2O3 ratios. Such anomalous values could be related to removal of CaO from Komatiites during fluid-driven hydrothermal alteration, thus lowering CaO/Al2O3 ratios. The elemental characteristics of Al-depleted Komatiites such as higher (Gd/Yb)N (>1.0), CaO/Al2O3 (>1.0), Al2O3/TiO2 ( 18) together with higher HREE, Y, Zr suggest their derivation from shallower upper mantle without garnet involvement in residue. The observed chemical characteristics (CaO/Al2O3, Al2O3/TiO2, MgO, Ni, Cr, Nb, Zr, Y, Hf, and REE) indicate derivation of the Komatiite and Komatiite basalt magmas from heterogeneous mantle (depleted to primitive mantle) at different depths in hot spot environments possibly with a rising plume. The low content of incompatible elements in studied Komatiites suggest existence of depleted mantle during ca. 3.2 Ga which in turn imply an earlier episode of mantle differentiation, greenstone volcanism and continental growth probably during ca. 3.6–3.3 Ga which is substantiated by Nd and Pb isotope data of gneisses and Komatiites in western Dharwar craton (WDC).
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3 35ga Komatiite volcanism in the western dharwar craton southern india constraints from nd isotopes and whole rock geochemistry
Precambrian Research, 2008Co-Authors: M Jayananda, T Kano, Jeanjacques Peucat, S ChannabasappaAbstract:Abstract We present field, petrographic, Sm–Nd whole-rock isochron and whole-rock geochemical data for Komatiites from Sargur Group greenstone belts of the western Dharwar craton. Field evidence such as pillow structure indicates their eruption in a marine environment. Petrographic data reveal that the igneous mineralogy has been altered during post-magmatic hydrothermal alteration processes corresponding to greenschist- to lower amphibolite facies conditions with rarely preserved primary olivine and orthopyroxene. A 16-point Sm–Nd whole-rock isochron gives an age of 3352 ± 110 Ma for the timing of eruption of Komatiite lavas. About 60% of the studied Komatiite samples show Al-depletion whilst the remaining are Al-undepleted. The Al-depleted Komatiites are characterised by high CaO/Al2O3 ratios (1.01–1.34) and low Al2O3/TiO2 (5–16) whereas Al-undepleted Komatiites show lower CaO/Al2O3 ratios (0.59–0.99) and higher Al2O3/TiO2 (17–26). Trace element distribution patterns of Komatiites suggest that most of the primary geochemical and Nd isotopic compositions are preserved with only minor influence of post-magmatic alteration processes and negligible crustal contamination. The chemical characteristics of Al-depleted Komatiites, such as high (Gd/Yb)N together with lower HREE, Y, Zr and Hf, imply their derivation from deeper upper mantle with garnet (majorite?) involvement, whereas lower (Gd/Yb)N slightly higher HREE, Y, Zr and Hf suggest derivation from shallower upper mantle without garnet involvement. The observed chemical characteristics (CaO/Al2O3, Al2O3/TiO2, MgO, Ni, Cr, Nb, Zr, Y, Hf, REE) indicate derivation of the Komatiite magmas from different depths in a plume setting, whereas sub-contemporaneous felsic volcanism and TTG accretion can be attributed to an arc setting. In order to explain the spatial association of Komatiite volcanism with contemporaneous mafic-felsic volcanism and TTG accretion we propose a combined plume-arc setting. Nd isotope data of the studied Komatiites indicate depleted mantle reservoirs which may have evolved by early (>4.53 Ga) global differentiation of the silicate Earth as suggested by Boyet and Carlson [Boyet, M., Carlson, R.W., 2005. 142Nd evidence for early (>4.53 Ga) global differentiation of silicate Earth. Science 309, 577–581] or extraction of continental crust during the early Archaean.
